Various communication receivers process received signal using different kinds of adaptive loops, e.g., phase tracking loops, automatic frequency correction loops, timing recovery loops, automatic gain control, channel equalization loops and others.
For example, U.S. Pat. No. 7,593,490, whose disclosure is incorporated herein by reference, describes a joint synchronizer and decoder that implements two decision aided processes, which are referred to as “decision aided candidate selection” and “decision aided synchronization and decoding.” Decision aided candidate selection may be used to select a carrier frequency offset by selecting among a number of candidates for this parameter based on an indication of decoding success. Decision aided synchronization and decoding may be used for phase tracking based on an indication of decoding success. Although these joint synchronizing and decoding techniques may be implemented together, they may also be implemented independently. The joint synchronizer and decoder may be implemented within a return channel receiver in a DVB-RCS system using turbo coding and quadrature phase shift key (QPSK) data modulation.
U.S. Pat. No. 8,036,289, whose disclosure is incorporated herein by reference, describes an iterative residual frequency and phase compensation apparatus for an OFDM system and a method thereof. The apparatus includes a first classifying unit for classifying symbol sequences by each subcarrier wave, a soft-decision calculating unit for calculating a soft-decision value of a data symbol using a soft-decision reliability obtained from iterative decoding performed by the iterative decoder, a classifying unit for classifying the soft-decision values by a carrier wave, a frequency estimating unit for estimating a residual frequency error of each carrier wave using the soft-decision value, a phase estimating unit for estimating an average residual phase error using the soft-decision value, a frequency and phase compensating unit for compensating frequencies and phases for input symbols of each carrier wave using the estimated frequency error and the estimated phase error, and a buffer for temporally storing the compensated symbols to provide it to the first classifying unit.
PCT International Publication WO 2010/138206, whose disclosure is incorporated herein by reference, describes methods for iterative timing recovery. The methods include processing an input signal using an FEC decoder, using some of the information from the FEC decoding process to estimate the phase of the symbol carrier, and correcting the phase for subsequent input signals. Another of the embodiments under the present principles provides for post-processing of the phase estimation prior to using the estimate for phase correction. Another embodiment is a post processor that comprises a filter, including a Kalman filter. Another embodiment includes using a priori information embedded in the input signal, such as a synchronization signal, to assist the phase estimation process.